1. Field of the Invention
The present invention relates to a print inspection device and particularly to ink ejection inspection for a type of printers in which printing is made by ejecting ink.
2. Description of the Related Art
Inkjet printers, which have been used conventionally, make a print by ejecting ink onto paper by means of heat or pressure. Printers of this type include an inkjet head group composed of a plurality of inkjet heads each having an array of nozzles from which ink is ejected. FIG. 9 is a plane view showing a configuration of the inkjet head group 10 in a conventional printer. As shown in FIG. 9, an inkjet head array is formed by as many as “n” inkjet heads H1-Hn staggered in two lines. Four inkjet head arrays 2C, 2M, 2Y and 2K line up in a paper transport direction, for ejection of inks in color C (Cyan), color M (Magenta), color Y (Yellow) and color K (Black). Some printers are provided with a backup inkjet head array for each color.
A problem in such a printer is drying up of ink which occurs in the nozzles while the printer is not in use. The dried ink clogs the nozzles and can cause poor ejection of ink. When this happens, cleaning operations of the inkjet head (e.g. purge cleaning and wipe cleaning) is performed. Purge cleaning is an operation in which clogged nozzles are cleaned by sucking. Wipe cleaning is an operation in which inks delivering to the inkjet head are cleaned by scrubbing. The inkjet head is more susceptible to damage by wipe cleaning than by purge cleaning. So, generally, wipe cleaning is performed only when purge cleaning has not successfully solved the problem of poor ink ejection.
In order to deal with poor ink ejection as described, following proposals are made: JP-A 11-254796 discloses an inspection device which includes a printer unit provided with an ink jet nozzle head, and an inspection unit provided with an imaging camera for inspection. The inspection unit enables a continuous inspection of the state of the print in synchronization with printing operation. JP-A 2000-52542 discloses a device incorporating a photo sensor, in which a light emitting element and a light receiving element are disposed in such a way that the optical axis is set at a predetermined angle with respect to a recording head nozzle array. Ink ejected from the recording head crosses the optical axis and varies photo sensor output, and this variation is used for ink ejection inspection. JP-A 2003-11336 discloses a method of inspecting of printing quality, in which a line is printed on a paper margin in continuous printing operation and imaging means captures an image of the line and this image is checked against a pre-registered image.
However, devices disclosed in JP-A 11-254796 and JP-A 2000-52542 are for moving-type recording heads, and not applicable to non-moving type (hereinafter called “fixed type”) in which a full-line recording head is fixed along the width of printing paper. The device according to JP-A 2003-11336 requires imaging means capable of capturing images as wide as the printing width, which requires increased cost when the printing width is large.